2010年12月大学英语四级考试全真预测试卷六Part I Writing (30 minutes)Directions: For this part, you are allowed 30 minutes to write a composition on the topic: Styles of Living. You should write at least 120 words following the outline given below in Chinese:1. 有些人愿意和父母居住在一起2. 有些人想自己独立居住3. 我的看法Styles of LivingPart II Reading Comprehension (Skimming and Scanning) (15 minutes)Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. For questions 1-7, markY (for YES) if the statement agrees with the information given in the passage;N (for NO) if the statement contradicts the information given in the passage;NG (for NOT GIVEN) if the information is not given in the passage.How Ice Cream WorksThe U.S. ice cream industry sells about a million gallons of ice cream each year, dispensing cones, gallons, pints, sundaes and other desserts through grocery stores and ice cream shops. In fact, eight percent of all the milk produced in the U.S. ends up in a frozen dairy product.Ice Cream or Frozen Dessert?Not just any frozen treat can be called ice cream. In fact, the U.S. Department of Agriculture has specific rules that define what can and cant be labeled ice cream. To bear the Meets USDA Ingredient Standard for Ice Cream stamp, it has to contain at least 10 percent milk fat, and a minimum of six percent non-fat milk solids. A gallon has to weigh at least 4.5 pounds.The range of milk fat (sometimes referred to as butter fat) used in ice cream can go from the minimum 10 percent to a maximum of about 16 percent. Most premium ice creams use 14 percent milk fat. Higher fat content leads to better, richer taste and a creamier texture. Ice cream makers dont go higher than 16 percent because it would be costly and very high in calories. An ice cream with this much milk fat would also taste so rich that people would probably eat it in smaller amounts, which would be bad news for people who sell ice cream for a living.Other frozen desserts, such as sorbets (果汁冰糕), low-fat ice cream, and frozen yogurt, are not technically ice cream at all. Frozen custard is ice cream that has at least 1.4 percent egg yolk solids, and soft serve can be any frozen milkbased dessert that has not gone through the hardening processmore on that later.In terms of specific ingredients, the recipe for ice cream is simple. But in scientific terms, its complicated stuff. Ice cream is a colloid, a type of emulsion(乳状液). An emulsion is a combination of two substances that dont normally mix together. Instead, one of the substances is dispersed throughout the other. In ice cream, molecules of fat are suspended in a water-sugar-ice structure along with air bubbles. The presence of air means that ice cream is also technically a foam.In addition to milk fat, non-fat milk solids, sugar, and air, ice cream also contains stabilizers and emulsifiers. Stabilizers help hold the air bubble structure together and give the ice cream a better texture. Although gelatin(凝胶) was originally used as a stabilizer, xanthan gum, guar gum, and other compounds are used today. Emulsifiers keep the ice cream smooth and aid the distribution of the fat molecules throughout the colloid. Egg yolks were once used, but ice cream manufacturers now tend to use other chemical compounds. These stabilizers and emulsifiers make up a very small proportion (less than one percent) of the ice cream.Making Ice CreamWhether its being made in your kitchen with a hand crank, at a local homemade ice cream shop with a stand-alone ice cream maker, or in a factory that cranks out thousands of gallons of ice cream every day, the process of making ice cream is basically the same. The only difference is the scale of the operation.First, you need ice cream mix. You can buy commercially made ice cream mix that is set to a certain milk fat content. Ice cream factories usually make their own mix by combining milk, cream and sugar in a 3,000 gallon vat, with the proportions and mixing controlled by computers. The mix is then pasteurized(用巴氏法灭菌), or heated, to kill any harmful bacteria. If you were to make your own mix at home, you could pasteurize it by cooking it in a double boiler, or use an egg substitute or pasteurized egg product. This step is important because otherwise people who eat your homemade ice cream could get sick due to salmonella contamination. According to the Centers for Disease Control, those most at risk include the elderly, very young children, and people with compromised immune systems.The next step in production is adding flavor to the mix. There are thousands of varieties of ice cream, so just about any combination of flavors is possible. From vanilla to cinnamon, chocolate to triple chocolate fudge brownie, it all gets blended into the ice cream mix. In a factory, this step takes place in vats that hold hundreds of gallons of ice cream, whi